The invention relates, in general, to machine tools, and in particular, to devices for holding at least one workpiece on the supporting surface of cutting machines, especially for use in repetitive production and/or preprogrammed machining.
Many mechanical operations require that one or more workpieces be held stationary for a period of time. Various types of clamps and other devices are known in the art for securing a workpiece in a desired position to facilitate an operation on the workpiece.
An apparatus for securing one workpiece at a time is disclosed in U.S. Pat. No. 4,805,888 to Bishop. The Bishop patent describes a two-piece adjustable clamp where the bolt-like portion of each clamp has a lower end threaded into a cooperating tapped hole of a platen, and has an eccentrically-offset upper end about which a shallow nut-like portion is socketed for orbital camming movements. However, Bishop has vertical walls where only one of the vertical walls can hold a workpiece laterally when the bolt-like portion is fastened to the platen.
Another apparatus for securely holding a workpiece is described in U.S. Pat. No. 5,310,299 to Bernstein. The Bernstein patent describes a clamping member having a concentric conical bore (i.e., a bore that is not offset) for receiving a fastener therethrough which when turned engages against the inner bearing surface of the conical bore providing a single lateral force which urges the clamping member toward a workpiece and a stop. Thus, the clamping device of Bernstein""s has only a single vertical surface which can hold a workpiece securely against a stop.
Accordingly, both clamping devices described by Bishop and Bernstein solely produce a single lateral or horizontal force for securing a workpiece against a stop on a platen which is inadequate for securing a workpiece during machining and only one side of both their devices can hold a workpiece. Consequently, these clamps and other known clamping devices have failed to secure workpieces when a cutting machine is removed from the workpiece. That is, when a cutting machine such as a drill or slitting saw is inserted into the workpiece there is usually no problem as the horizontal or lateral force holds the workpiece; but, when the drill or slitting saw is removed, the workpiece pops or jumps out of the clamp.
Furthermore, in addition to the downtime caused by the workpiece or several workpieces jumping out of the clamp, the jolt which causes the workpieces to pop out also causes damage to the clamp. Thus, considerable time and money are lost in replacing the workpieces and the clamps due to this prior design.
The above problem was solved with the gripping device which is disclosed in U.S. patent application Ser. No. 08/555,869, filed Nov. 13, 1995. That application is incorporated herein by reference.
U.S. Pat. No. 3,473,420 to Boggs shows an apparatus for positioning and clamping one or more workpieces. However, three points of contact are required to hold each workpiece and thus, at least two positioning blocks are need to secure a single workpiece. As a result, a large portion of the platen or jig is devoted to positioning blocks or stops and not to the workpieces. Consequently, a longer time is required to secure each block, and, additional expense is incurred in the use of the larger or more platens that are needed to secure the workpieces.
Applicant is aware of a two-piece clamping device which is produced under the name KIRK VISE. However, that clamp employs rubber parts and lacks an offset bore and thus the clamp is limited in what it can hold down and further has too much travel. Morever, this clamping device breaks down after limited amount of use causing downtime and additional expense in replacing the worn clamping devices.
The present invention overcomes the above problems by providing a device having a fixture with a working surface and at least one hole, at least one stop rising above the working surface, a fastener, a gripping member having a first block portion and a second block portion where the first block portion is joined to the second block portion for relative movement, each block portion has an inner wall and a gripper wall adapted to engage a workpiece, the inner walls of the first and second block portions form a through bore for receiving the fastener when the first and second block portions are joined and each inner wall has a lower radial surface and an upper conical surface, a portion of the upper conical surface is less recessed than the other portions of the upper conical surface whereby at least one of the first and second block portions of the gripping member slides toward the at least one stop and the gripper wall of the respective block portion applies a downward inward holding force on a workpiece when the fastener bears against the less recessed portion of the respective at least one block thereby creating the downward inward holding force and securing the fastener to the at least one hole of the fixture.
Accordingly, it is an object of the present device for holding at least one workpiece while a workpiece is being worked on by a machine.
Another object of the invention is to provide two parallel, spaced-apart stops and the at least one hole of the fixture is positioned between the parallel stops so that both gripper walls of the first and second block portions can secure workpieces to the fixture.
The holding force or forces of the invention may be achieved by a gripper wall having an upper and lower section where the upper section applies the holding force.
It is a further object of the invention to have a gripper wall which is potentially tapered from the upper section to the lower section.
It is yet another object of the invention to provide biasing means for joining and biasing together the first and second block portions against relative movement. The biasing means tends to evenly distribute the holding forces on the workpieces when two workpieces are held on either side of the gripper and also facilitates release of the gripper walls away from the workpieces when the gripper fastener is raised.
It is still a further object of the present invention to provide a gripping member for holding at least one workpiece on a fixture which includes a first block portion having an inner wall and a gripper wall, and a second block portion having an inner wall and a gripper wall where the first and second block portions are joined for relative movement and the inner walls of the first and second block portions form a countersink and a through bore when said first and second block portions are joined. The offset-countersink has first and second conical surfaces where the first conical surfaces are less recessed than the second whereby at least one gripper wall applies a downward inward holding force on a respective workpiece when a fastener secures gripping member to a fixture.
According to the present invention, a gripping member is provided for holding at least one workpiece on a fixture which includes first and second block portions, each block portion having an inner wall for forming a through bore for receiving a fastener when the first and second block portions are joined and a gripper wall adapted to engage a workpiece. Each gripper wall may be tapered inwardly from an upper edge to a lower edge depending on the workpiece to be engaged so that the gripper wall applies the appropriate downward inward force on a workpiece when a fastener secures the gripping member to a fixture.
The invention will become more fully apparent from the claims and the description as we proceed in connection with the drawings.